This project is designed to determine whether the ability of short peptides to bind to antibodies raised in response to native protein is related to their conformational flexibility. Data from which we can derive information on the energy and entropy of interaction for antigen - antibody interactions and the extent to which conformational flexibility contributes to the binding of a number of synthetic peptide antigens to monoclonal antibodies will be obtained from equilibrium studies. The association energy of the whole protein with monoclonal antibody will also be measured to compare the affinities of the isolated epitopes with those stabilized within the native molecule. Theoretical and experimental estimates of the conformational space available to these peptides will be made to establish whether the association energy can be accounted for purely on the basis of non-covalent interactions between complementary conformations of combining site and ligand or whether the entropy of a statistical ensemble of peptide conformations has to be overcome to induce native conformation in the peptide on binding to antibody. In either case it will be assumed that the conformation of the peptide bound to immunoglobulin is that of the same sequence in the native protein. Assays of the residues required for binding, together with conformational information, will be used to model immunoglobulin combining sites in order to estimate the nature and number of interactions necessary to bind synethetic peptides to antibody. These models will be developed to be consistent with measurements of the entropy and free energy of association of the equilibrium. Initially this study will concentrate on known antigenic peptide sequences from two proteins, cytochrome c and lysozyme. Preliminary studies presented in this proposal will describe two synthetic antigenic peptide sequences from cyt. c and the residues which are necessary for their binding to antibody. Methods of delineating synthetic peptide epitopes from lysozyme, in order to determine the residues directly interacting with antibody, are described.